WET COFFEE PROCESSING AGRO-INDUSTRY WASTEWATER TREATMENT POTENTIAL OF CONSTRUCTED AND NATURAL WETLANDS : THE CASE OF KEGE PROCESSING PLANT IN SIDAMA NATIONAL REGIONAL STATE, ETHIOPIA

Abstract

Constructed wetlands are engineered to use natural processes to remove pollutants from contaminated water in a more controlled environment, using phytoremediators for effective wastewater treatment.The aim of this study was to establish the coffee berries processing AgroIndustry Wastewater Treatment Potential of Constructed and Natural Wetlands.The finding indicates that calcium had the highest concentration (1355±18.02mg kg-1 ) of macro elements in soil samples (from the farmland), followed by K (681.43±1.52mg kg-1 ). Similarly, Na (111.63±0.35 mg kg-1 ), Cu (49.96±0.99mg kg-1 ), Co (5.43±0.31 mg kg-1 ), Mn (0.62±0.238mg kg1 ), Ni (0.194±0.01mg kg-1 ), and Zn (0.163±0.007mg kg-1 ) were detected among the microelements in soil samples (from farmland). Pb and Cr were not detected in all soil samples (from farmland). Potassium (K) was found to have the highest concentration (99.93±0.037mg kg1 ) followed by Ca (17.23± 0.36 mg kg-1 ) among the macro elements in coffee beans from farmers’ farms. Like coffee beans from farmland, samples from washing plants also contained the highest K (77.93±0.115mg kg-1 ), followed by Ca (4.33±0.035 mg kg-1 ). Metal levels in coffee bean samples from farmland are in the following order: K>Na>Ca >Mn>Cu> Ni>Zn. Metal levels were found to be K>Na>Ca >Mn>Cu> Zn>Ni in coffee beans from the washing plants. Co, Cr, Pb and Cd were not detection in all coffee bean samples. Except for calcium, potassium and manganese, the levels of metals in coffee beans from farmland and washing plants were not significantly different at a 95% confidence level within a kebele. Findings indicated that a natural wetland had a mean influent and effluent of total suspended solids (TSS) of 2190.78±448.46 mg/L and 972.67±234.312mg/L, respectively. A Mann-Whitney U test revealed that TSS was significantly higher in the natural wetland (median =1551.50) compared to constructed wetland (median =922.5), U =676.5, z=-2.435, p=0.015, r=0.257. Natural wetlands had a mean influent of biological oxygen demand (BOD) was 4277.94±157.02mg/L, while in the effluent the BOD it was 326.83±112.24 mg/L. In constructed wetland it was 4192.4±191.3mg/L, 782.72±507.6mg/L and 88.28±20.08mg/L in influent, middle and effluent respectively. The average chemical oxygen demand (COD) value at influent in natural wetlands was 8085.61±536.99 mg/L and in the effluent it was 675.33±201.4mg/L. In the constructed wetland, it was found to be 8409.8±592.9, 1372.6± 387.94, and 249.0± 7.68 for influent, middle and effluent respectively. Comparatively, the purification efficiency of organic pollutants (TSS, BOD, and COD) of constructed wetlands was better than natural wetlands, whereas natural xvii wetlands had better purification efficiency of nitrogen compounds such as ammonium, nitrite, and nitrate. On average, removal rates for nitrogen compounds were 39.53% and-24.41% for ammonium, 79.44% and 55.4 % for nitrite, and 68.90% and 60.6% for nitrate in natural and constructed wetlands respectively, while the phosphate removal rate was 43.17% and 58.7 in natural and constructed wetlands, respectively. A Mann-Whitney U test revealed that there is no significance difference in nitrite, nitrate, ammonium, and phosphate concentration between natural and constructed wetlands (p >0.05). Findings indicated that Ca (460.0 ppm) had the highest mean concentration of heavy metals, whereas Ni (0.50 ppm) had the lowest in soil samples of constructed wetland. Metal absorption by Vetiver Grass is the highest concentrations found in plant tissues grown in the following order K > Ca > Na > Mn > Fe > Zn > Cu > Ni > Cr in shoots. The order of the heavy metal contents in the roots of vetiver grass was K > Ca > Na > Mn > Fe > Zn > Cu > Ni > Cr. Based on translocation and bioconcentration factors, the plant was found efficient in the translocation of Mn and Ni from roots to shoot, whereas It served as a potential phytostabilizer for Ca, Cu, Cr, Fe, K, Na, and Zn since the TF values are lower than 1, which show that vetiver grass prefers to accumulate heavy metals in the roots rather than the shoot and so supports its potential for phytostabilization. From the present study, it was evident that vetiver grass is an ideal candidate for wastewater treatment using constructed wetland technology. Based on these results, both systems of treatment were effective in treating the coffee effluent since most of the values obtained were below the permissible EEPA limits. Even though the constructed wetland treatment plant performed better overall, in comparison, the natural wetlands had better purification efficiency for nitrogen compounds like ammonium, nitrite, and nitrate and the constructed wetlands had better purification efficiency for organic pollutants (TSS, BOD, and COD). We observed permitted levels of macro and trace elements in coffee beans from farmlands and washing plants. Only in the soil samples, cadmium concentrations are higher than those permitted for agricultural soil recommended by WHO and FAO. Overall, there is no health danger linked with the use of coffee beans due to detrimental and trace heavy metals